Make it more than just a scar, maybe it has to be done by a certain person or in a certain way? I don't really see the problem, honestly. I made a game where a huge part of the magic system was brands that the priests could give you.
As I was saying earlier,
That being said, people use Meyers-Briggs as an inteligance thing? It was never meant to be that way... that's just wrong.
I think it works fairly well, but in the basic 4 letter simplification you get less variation than if you see the number scale attatched. Some people aren't strong one way or the other with one or more of the letters (myself included) so it doesn't make as much sense to them.